Done work on two Shadow Troopers and one Stormtrooper so far. I don't strip, but I do sand everything, including filing off the mould lines and filling the minor divots resulting from interior structures, since sanding shows all those up nicely. Since the "real" helmets have the top and back as one piece, I recreate that with epoxy and filler putty on that seam. And since these helmets have an upcurved brow versus the level brow of the movie props, I bring that down in various ways, depending on the end result I'm working toward. Plus the matter of the side tubes -- the slits are wrong and need to be redone for Rogue One/Solo accuracy, and need to be filled for an OT retro-build. Not getting into other details. So all of that needs to get painted over anyway, and sanding helps smooth and blend all of that. Plus aiding paint adhesion.